Temperature change responsive means for controlling electric circuits



March 18, 1952 w. H. RUFFLE 2,589,869

TEMPERATURE CHANGE RESPONSIVE MEANS FOR CONTROLLING ELECTRIC CIRCUITSFiled 001;. 22, 1949 2 SHEETSSHEET l 17v INF/1701C 3 W X34, y 6;

Mil-I8 7 19491212 21,954.;

w. H. RUFFLE E CHANGE RESPONSIVE MEANS March 18, 1952 2,589,869 YTEMPERATUR FOR CONTROLLING ELECTRIC CIRCUITS 2 SHEETS-SHEET 2 Filed Oct.22, 1949 QUE mmw m w jwl Patented Mar. 18, 1952 TEMPERATURE CHANGERESPONSIVE MEANS FOR CONTROLLING ELECTRIC CIRCUITS William Harry Rufiie,Hove, England, assignor to Speed Development Company Limited, Hove,England, a British company Application October 22, 1949, Serial No.122,887 In Great Britain March 11, 1949 20 Claims. 1

This invention relates to a relay-embodyingcircuit with one or morehighly sensitive or millivolt type switches for afiording a warning oralternatively controlling appropriate apparatus upon a change in ambienttemperature at a control zone, and in which devices such as e. g.thermo-couples which are very sensitive to changes in ambienttemperature are connected to the electrically energised operatingelement of the switch, e. g. a coil of a switch constructed after thefashion of a milli-vclt meter, is adapted to actuate the switch so as tochange from a normal or inoperative position to an operative position soas to bring into circuit relays.

With control circuits embodying a highly sensitive switch, e. g. aswitch constructed after the fashion of a milli-volt meter and which isoperated by energising the sensitive coil therein, the switch is foundto be unreliable in operation. For example, assuming that the movingcontact of the switch is displaced by reason of the energy developed atthe thermocouple, the direction of flow of current from the normalsource through the hair spring of the switch can be such as to implementthe current generated by the thermocouple, so that the switch mightperform satisfactory for one switch stage in the operation. However, onthe moving contact of the sensitive switch returning to the normal orresting position due to the reduced output of the thermocouple, at themoment of contact, the implemented E. M. F. introduced into the switchhair spring circuit is still in the same direction to that generated bythe thermo-couple, with the result that at the moment of contact thetendency is for the moving contact to leave the normal or restingcontact due to the added E. M. F. induced in the hair spring.Accordingly, one object of the present invention is to provide a circuitwhich obviates the foregoing disadvantage and ensures a positive holdingof the moving contact against both of the co-operating contacts in theproper sequence, whereby the apparatus can be adopted with confidence asto its reliability for producing signals or controlling apparatus underconditions demanding great efiiciency, e. g. on aircraft for givingwarnings of the outbreak of fire and/or for the remote controllingautomatically of suitable apparatus such as e. g. heaters, coolers andfire extinguishers.

Another object of the present invention is to combine with the apparatusa test circuit whereby when the apparatus is used with a plurality ofcontrol points, e. g. as with the power units of aircraft, by operationof a signal switch on instantaneous indication of the effectiveness ofthe circuits appropriate to all of the control points' is obtained.

Having regard to the foregoing the present invention is characterisedbroadly in that means is provided whereby when an E. M. F. is developedat the device which is very sensitive to temperature changes, e. g. athermo-couple, to actuate the switch, upon the moving member of theswitch reaching its terminal or contact engaging position there isintroduced an implemented E. M. F. which adds effectively to the outputof the said very sensitive device, and when the output of the said verysensitive device falls so that it cannot overcome the influence of themeans tending to return the contact to its original position when themoving contact reaches the terminal return position, an implemented E.M. F. is introduced in the reverse direction to that generated by thesaid very sensitive device to still further reduce the resistance to there-assertion of the aforesaid means which returns the contact to itssaid original position.

In order that the invention may be clearly understood and readilycarried into effect drawings are appended here to illustratingembodiments thereof, and wherein:

Figure 1 is a diagrammatic view showing the invention as adapted for usewith a single control source.

Figure 2 is a diagrammatic view showing the invention as adapted for usewith a plurality of control sources, and

Figure 3 is a sectional elevation of a suitable form of thermo-coupledevice for use with the present invention.

Referring to Figure 1 of the drawings the control source C. S. fromwhich a warning or other signal is to be derived is shown as embodying aplurality of thermo-couples arranged in series, that is to say a chainof pairs of thermo-couples 5a, 51), although of course only one pair ofthermocouples may be employed where a simple single control source iscontemplated. By way of example in Figure 1 the chain of thermo-couplesillustrated can be assumed as being assembled at various vulnerablepoints on an aircraft engine. The thermo-couple devices are of identicalform throughout, each device having its pair of thermo-couples 5a, 5bboth exposed to the infiuence of normal ambient air conditions but one(5b) being shrouded by shroud 5 and the other (5a) clear of the shroud,or more fully exposed, so that the latter will be affected first by theeffect of a very sudden change in temperature, e. g.

3 due to outbreak of fire. That is to say these thermo-couples areself-compensating at a normal or gradual rise of temperature andconsequently under these conditions the output of one thermo-couple acancels out the output of its mate 5b.

In the event of flame, or an abnormal temperature rise, impinging on theexposed thermocouple Ea, the output of this thermo-couple will exceedthat of the other, and the resultant E. M. F. i. e. the amount by whichthe exposed thermocouple P. D. exceeds that of the other is applied tothe moving coil l of a milli-volt switch i. The switch l is of thehighly sensitive type, c. g. constructed as shown after the fashion of amoving coil milli-volt meter, in which the mo"- ing contact is a needleheld in engagement with a fixed contact 3 by a hair spring 1.

The application of the aforesaid low E. M. F. to the moving coil "1 ofthe switch overcomes the hair spring i and moves the needle contact 2from the contact 3 into engagement with another fixed contact 6, andthereupon there is set into operation relay means which enables a sourceS, e. g. a 24 volt D. C. supply as used on aircraft, to actuate awarning device, such as the lamp L, or other suitable device which forits operation must consume more energy than is obtainable simply fromthe thermo-couples of the control source C. S.

The said relay means comprises a double wound relay L having a winding 8and an oppositely Wound winding the winding 8 being connected by l adiii to the fixed contact 5 and to the negative or return to source S bylead H, the positive connection to the winding 8 being via lead Iii,contact 8, needle contact 2, resistor R lead so closed contacts is, Eli,lead 9:: and main lead 9 to the positive of source S via resistor R thiscircuit including a pair of contacts so which are regularlyintermittently opened and closed to introduce a pulsating supply to theneedle contact 2. There is only a momentary loading of the neediecontact 2 due to the fact that when a warning is to be given (or otherapparatus brought into operation) by reason of the very low E. M. F.output from the thermo-couples upon the contact 2 moving over intoengagement with contact G, and the winding 3 being energised from thesource S, a of holding contacts i2 and I3 associated with this windingare closed to trans fer the electrical load from the contacts 2 and 5 toa holding circuit.

The said holding circuit comprises lead 30; ,4

from main positive lead 9 via the resistor R to contact contact !2, leadlZa, winding 2% and return leadv ii. The Warning lamp L is brought intocircuit by reason or" the closing of a pair of contacts El and 22operated in unison with contacts !2 and t2, the contact 2| beingconnected to the lead 9 and the contact 22 being connected by lead 22ato the lamp L and viev lead 38 to the return lead 2 5.

Obviously, in a switch constructed after the manner of a moving coilmilli-volt meter as is contemplated in the present invention, thecontact pre. .ure is exceedingly light, hence as aioresaid, it isdesirable to obtain a very positive engagement of the moving needle 2,with each of the contacts 3 and 5 the moment of contact, and for thispurpose -le present invention provides means to implement the electricalenergy overcoming the influence of the hair spring :2 at the moment whenthe contact 6 is engaged, and, in the reverse direction, to reduce theE. M. F. opposing the influence of the hair spring, so that in ei fectan assisting E. M. F. is introduced for both moments of contact in thecircult of the moving coil 7 in the correct direction to assist themaintenance of the milli-volt switch contacts until they have fulfilledthe function of either operating or releasing the relay L The saidimplementing E. M. F. is obtained from the source S by the introductionof the aforesaid r'sistcr R in the operating circuit which resistor,assuming we are dealing with a 24 volt source S, can have a value of 8ohms, and can be fixed as shown in Figure 1, or may be variable as shownin Figure 2. The current how, at the moment of contact, to the resistorR (which is in series parallel with the thermocouple chain), is split,part of it flowing through the resistor R and part of it through thethermocouple chain via leads 28b, 28a, to the moving coil 5 of theswitch 1 which is already under the influence or the output of thethermo-couple which of course corresponds to the amount which output of5c exceeds that of its mate 5b. As this implementing E. M. F. is in thecorrect direction i. e. in a positive direction through the coil l toassist the output of the thermo-coupics, at the moment of engagement ofthe moving contact 2 with the fixed contact 6, the output of thethermo-couples and the consequent energy in the moving coil is increasedby the amount introduced into the thermo-couple circuit from the normalsupply source S, In this connection, it will be seen that the lead 9from the normal supply source S is taken to one side of thethermo-couple chain, the resistance R being in series with the lead 9from the normal source and the moving contact, and in parallel with thethermo-couple chain circuit and the coil 7 of the switch, 1. e. aseries-parallel connection.

It will be seen that the said holding circuit is isolated from thepulsating circuit whereby a constant warning light is given. However, ifdesired the lamp circuit canbe broken intermittently via subsidiarycontacts on the pulsating relay.

Connected across the said winding 8 of the double wound relay L is aresistor R adapted to reduce the current flow through the winding 8 inpreparation for completing the circuit necessary for the requirements ofa subsequent release circuit This said winding 8 of the double woundrelay L is effective for performing both functions of operating therelay and transferring the electrical load from the switch contacts 2and 5 to the holding circuit aforesaid.

The value of the resistor R in relation to the circuit as a whole issuch that only a potential of say six volts is applied to the winding 8to hold it, the remaining volts said eighteen volts of a twenty fourvolt supply, being developed across a limiting resistance R in the mainfeed 9.

The moving contact 2 is now only held against the contact by the verylow E. M. F. from the thermo-couple. but when the thermo-couple outputis reduced to the normal state, i. e. the state appropriate to themoving contact 2 of the switch into engagement with the contact 3aforesaid, as e. g. when the flame previously causing the low E. F.output from the thermo-couple heing e; anguished, taking intoconsideration the influence of the switch spring 6 the lower contact 3will be one d, this will bring into circuit the other winding of thedouble wound relay L The circuit now is from lead 9, switch button l8,lead ll, winding l4, contacts I5 and 16 (which could now be closed dueto operation of the relay L lead 16a, contacts 3 and 2, resistor R (inparallel with coil 1 and the thermo-couple chain) lead 9b, contacts I9,20, lead 90, lead 9:11, pulsing contacts 9a, lead 9y, lead l3a, contactsI3 and 12, lead 12a winding 8 and resistor R in parallel, and fromthence to negative via lead II. In this connection it should bementioned that the moving contact 2 of the switch is now at a potentialof, taking the aforesaid example of a 24 volt source S, eighteen voltswith respect to positive of the source S, and, as the aforesaid holdingwinding 8 of the double wound relay L has only six volts across it, theeighteen volts supplied in the reverse direction to the other winding Id of this relay L must cause the relay L to release, the release of thesaid relay L breaking first the holding contacts l2 and I3, as well asthe lamp contacts 2| and 22, and in immediate succession thereto thecontacts l5 and [6, thereby causing the eighteen volts to disappear,this resulting in the only electrical energy now flowing in the circuitbeing that normally generated by the thermo-couple. The contact springsof the double wound relay L are so adjusted as to open contacts !2, 13,2| and 22 momentarily in advance of opening contacts l5 and I6.

As the operating winding 8 of the double wound relay L is connected tofull negative by lead H and is energised by a positive applied via thelimiting resistor R (which may be of a value of 800 ohms), the movingcontact 2 and contact 6 of the switch I during the initial operatingperiod, and as that during the other or release" period, the releasewinding [4 of the double wound relay L is connected to positive by lead[1, and the moving contact 2 of the meter switch is now at eighteenvolts negative with respect to this positive due to the volts developedacross the resistor R by virtue of it being in series with winding 8 andresistor R in parallel, it will be understood that the E. M. F. in-

duced in the aforesaid series parallel circuit is, at the releaseperiod, in the reverse direction to that obtaining when the movingcontact 2 and contact 6 engage.

The means for constantly intermittently making and breaking the circuitto the contact 2 and lead It! to the relay 8 comprises the pulse circuitcontaining the relays L L and L this pulse circuit interrupting atregular and frequent intervals the operating supply in lead 9.1: viacontacts 9a to the aforesaid double wound relay L during operating andrelease stages to prevent misoperation of the switch due to vibration.

The pulsating relays L L and L are connected across the twenty four voltD. C. supply via resistors R which can have a value of 2200 ohms each,the current being supplied from the continuous supply side of the lead 9via a lead 911 to coil of relay L via 9e, resistor R to negative. On theoperation of relay L contacts I are closed and the supply goes from 9dvia contacts Z lead 9 coil of relay L resistor R to negative. Theoperation of relay L opens contacts I which removes the short circuitfrom the coil of L L operates via lead 9d coil of L lead lift toresistor R The operation of L closes contacts I which places a shortcircuit across the coil L which causes L to release, which in turn opens1 contacts, thereby releasing L to close contacts I which short circuitscoil L- to release it and open contacts 1 to remove the short circuitfrom L which then re-operates and the sequence is repeated. By adoptingshort-circuiting method of releasing the relays a distinctive lag iscreated due to the comparatively slow collapse of flux in a closedcircuit.

The aforesaid test button 18 is for the purpose of obtaining a readyindication that the apparatus is in working order, this test buttonbeing provided in association with a relay L the energising of whichrelay via lead ll, button contacts l8a, 13b and lead 3i followingdepression of the button l8, opens contacts l9 and 20 and removes ashort circuit from a resistance R in series with the thermo-couple andcoil 1 circuit. This introduces into the thermo-couple chain an E. M. F.equal to the warning output 'of the thermocouples because the milli-voltswitch side (i. e. point 1 of the resistor R is connected to thenegative supply (lead H) via lead Ila through resistor R which can be of9100 ohms, and the other end of resistor R is connected via 9x, contacts9a lead 93 resistor R to positive. This introduction of the said E. M.F. in the thermocouple chain and consequent excitation of coil 1 willcause the contact 2 to engage contact 6, and as already indicated, thiswill result in contacts l2 and [3 being closed and the transfer of theload to lead l3a and return lead I l, and the contacts 2| and 22 willconnect lead 22a, lamp L and lead 30 to return H.

A multiple-plug connector (plugs 23 and sockets 24) is provided forconnecting up the relay apparatus to the warning lamp circuit and thesupply source S, and the lamp unit can be plugged in by plug contacts 33and 34.

When the apparatus is to be adapted to a plurality of control points,the single warning lamp L and switch I will be substituted by a numberof lamps and switches l and double wound relays L with associatedcircuits corresponding to the number of control sources. By way ofexample in Figure 2 four control sources are shown, e. g. two port andtwo starboard aircraft engines. However, as regards the pulsatingcircuit, the same number of relays L L and L will still obtain, and eachof these relays will actuate its own pair of contacts 9a to cover threeof the switch circuits, the fourth switch circuit being satisfied simplyby adding to one of the relays, e. g. the relay L in Figure 2, a furtherpair of contacts 9A. A further slight modification in thismultiple-control source circuit consists in the use of a separateplug-in connection 25 for the control source. Breeze type plugs orsockets 26 are provided for connecting the thermo-couple chains of thetwo engines on the port side to two of the circuits, and a likearrangement 2'! being adopted for the starboard side, so that from eachsocket or plug two pairs of leads 28a, 28b and 29a, 292) are taken, onelead 28a, 29a of each pair being connected to the associated switch coil1 and the other lead 28b, 29b to the lead 9a: communicating with themoving contact via the lead 90, contacts 2e, 19, lead 922 and thevariable resistor R between which and the point of connection of thelatter mentioned lead 912 from the thermo-couple is interposed theresistor R having a value of 8 ohms.

It is only necessary to employ one push-button l8 and one relay L fortesting all of the switch circuits, the relay L controlling all of thecontacts I9, 20 of the four circuits. By distinctively indexing thewarning lamps the operator 7 will be able to ascertain if any particularcircuit is not functioning.

In addition to operating the auxiliary relay L to introduce theequivalent P. D. into the thermocouple chain, the test button [8 alsoremoves the supply from the release windings M of the aforesaid doublewound relays L to obviate their functioning and giving a false clearsignal due to the engagement of the moving contact 2 and contact 3 ofeach of the milli-volt switches l during the break period of the pulsecurrent introduced as a substitute for thermo-couple output.

The normally broken contacts i5 and 16 of the double wound relay(Figure 1) or relays (Figure 2) obviate any accidental false operationof the double wound relays on their release windings I' l due to thefact that the positive leads 9 to the release windings are arranged incommon outboard of the release button.

In order to obtain highly sensitive and very responsive action at thecontrol source the form of thermo-couple shown in Figure 3 is preferablyadopted in the thermo-couple chain. Each thermo-couple comprises twolengths of wire 5! and 42 attached at one end to an insulating base disc43 and having connected across their other ends at points it and 45 adissimilar wire element 46 to provide two spaced points or Zones ofgeneration of low E. M. F. Shrouding this arrangement of wires is acylindrical metallic sleeve 41 integral with a hollow cylindrical cap 48accommodating the insulating base disc 43 and a cover disc 49 also ofinsulating material, a base plate 50 being secured to a flange 51 of thecap t8 by screws 52.

The elements 46, 45 and can be arranged as two chromel-alumelthermo-couples in opposition so that with normal slow temperaturevariations little voltage output is obtained. With any rapid rise oftemperature however, as in the case of a fire, the outer exposedthermo-couple becomes hotter than the inner protected one, and thevoltage generated operates the appropriate moving coil relay to give awarning. When this rapid rate of rise ceases the diiference intemperature between the inner and outer thernio-couples decreases, andthe warning is cancelled.

The cap 48 is slotted or otherwise suitably apertured as at 53 for thefree access of ambient air or gas to the assembly or" wire elements, theupper point 45 of the thermo-couple device being exposed above or closeto the rim of the sleeve 41 but protected from injury by upstanding lugs54 of such sleeve.

Threaded upon the wire elements 32 and s5 is a disc 55 of insulatingmaterial having a clearance from the sleeve il forming a screen betweenthe points 44 and 35. Hence, the point 45 is more exposed than the point44 to the direct influence of flame in the vicinity of the device. 1

Whilst the slotted cap 48 freely admits ambient air or gas to theinterior of the sleeve 41 so that normally the points of thethermo-couple device are exposed to the same temperature condition, suchslotted cap will act as a muiiie to prevent access of flame through theslot 53, so it is immaterial in which direction the flame plays upon thedevice in order to ensure that the point 45 will be subjected to theinfluence of the flame in advance of the point is in order to obtain thedesired momentary distinctiveness in temperature at the points M and $5.

vThe various relays and switches are mounted in a chassis supported inturn by rubber dampers in a housing or on a base plate so that if theapparatus is subjected to vibration, the vibrations will be damped orabsorbed by the rubber dampers.

I claim:

1. In combination a milli-volt switch with a normal conditions contact,an operative circuit contact and a moving contact, means responsive tosudden temperature change to develop a very low E. M. F. of afew'milli-volts and connected to said switch to actuate the movingcontact, an electrically operated appliance adapted to be actuated froman operative source of electrical energy having a much greater E. M. F.output than the said means, electrically operated means normallyisolated from the switch but adapted to connect said appliance to saidsource and adapted to be fed from said source, means controlled by theactuation of said switch due to sudden temperature change to effectivelyconnect said electrically operated means momentarily via said switchmoving contact to said higher E. M. F. source and thereupon to isolatesaid moving contact from said higher E. M. F. source, and means to feedfrom said higher E. M. F. source an implementing E. M. F. to assist inproper operative engagement of the moving contact with the operativecircuit when the moving contact is actuated to bring in the operative.circuit, and means to feed also from said higher E. M. F. source animplementing E. M. F. to assist in proper engagement ofthe movingcontact with the normal conditions contact when the moving contact isactuated in the direction to engage the normal conditions contact.

2. Electrically operated apparatus for bringing into operation by reasonof a suddenchange in temperature at a control source an electricallyoperated warning device, comprising a thermocouple for location in saidsource so as to generate a low E. M. F. output, a switch having a fixednormal conditions contact and a fixed operative circuit contact and alsoa co-operating moving contact actuated by said low E. M. F. output ofthe thermo-couple, a relay, means to connect said relay to a normalsource of .supply of electrical energy via said moving contact and saidoperative fixed contact so as to energise said relay when the said lowE. M. F. is generated to engage the moving contact with the latter fixedcontact, a holding circuit connected to said relay and adapted'to be fedfrom the normal source, a warning device or other suitable electricallyoperated appliance in said holding circuit, means actuated by said relayto bring in said holding circuit and cut out said switch so that thesaid relay is thereupon energised via the holding circuit, a pulsatingcircuit fed from said normal source and located in the connection fromthe normal source to said moving contact and operating independently ofthe holding circuit, a resistance in series parallel with the circuit ofthe thermo-couple and switch and located in the connection from saidnormal source to said moving contact which splits the resultant E. M. F.so that part of the E. M. F. flows through said resistance and partthrough the moving contact actuating means to implement the E. M. F.operating the moving contact, a supply lead in said holding circuit tosaid relay and a return lead connecting the said relay to the warningdevice or other electrically operated appliance, and a further relayadapted to be brought into circuit when the normal conditions contact isengaged by the moving contact and connected to said normal source of E.M. F. supply at a potential with .respect to the other relay which willovercome the energy derived from said latter relay and introduce anassisting E. M. F. into the means op erating the moving contact whenactuated back into engagement with the normal contact, a test circuitwith means to bring it selectively into operation, and a furtherresistance connected across the thermo-couple circuit and the return tothe said normal source of E. M. F. adapted upon bringing in the testcircuit to introduce into the thermo-couple circuit an E. M. F. equal tothe output of the thermo-couple circuit obtaining when the switch isactuated to bring in the first mentioned relay.

3. In combination a plurality of milli-volt switches, means adapted tobe located at a plurality of independent control sources and responsiveto suddent temperature change in any one of the control sources toproduce a very low E. M. F. of a few milli-volts and connected to saidswitches to actuate one of the switches upon a sudden temperature riseat one of said control sources, an electrically operated appliancecommon to all of said switches adapted to be actuated from an operativesource of electrical energy common to all of said switches and having amuch greater E. M. F. output than the said means, electrically operatedmeans with each switch to connect said appliance to said operativesource and adapted to be fed from said operative source, meanscontrolled by the actuation of each switch due to sudden temperaturechange to effectively connect the associated said electrically operatedmeans momentarily via the associated switch moving contact to saidhigher E. M. F. source and thereupon to isolate said moving contact fromsaid higher E. M. F. source, and means to feed from said higher E. M. F.source an implementing E. M. F. into the means actuating the switch whenthe switch is actuated to bring in the said appliance and when it isactuated to cut out the said appliance.

4. In combination with a milli-volt switch, means responsive to suddentemperature change to produce a very low E. M. F. of a few milli-voltsand connected to said switch to actuate the switch, an electricallyoperated appliance adapted to be actuated from an operative source ofelectrical energy having a much greater E. M. F. output than the saidmeans, a holding circuit for the appliance normally isolated from theoperative source of electrical energy and said switch, a double woundrelay having one winding controlled by the actuation of said switch dueto sudden temperature change to efiectively connect said electricallyoperated appliance to said higher E. M. F. source whilst transferringthe load due to said source from said switch to said holding circuit, apulsating relay regularly interrupting the current supply to the switch,a resistor in parallel with said low E. M. F. producing means connectedto the switch and in series with said operative source and the switch toproduce splitting of the resultant E. M. F. developed across the saidresistor so that part flows through the resistor and part through saidlow E. M. F. producing means to feed from said higher E. M. F. source anassisting E. M. F. into the switch actuating means when the switch isactuated to bring in the said appliance, a resistor connected acrosssaid winding adapted to reduce the current fiow through the winding, arelease circuit adapted to feed an assisting E. M. F. into the switchwhen the switch is returned to normal and including the other winding ofthe said double wound relay, contacts with said two windings, thecontacts of the first mentioned winding being closed to bring in thesaid holding circuit and the said appliance, the contacts of the windingof the release circuit connecting such winding to the switch and throughboth of said resistors to the return side of the said higher E. M. F.source, and a resistance in the supply to the first mentioned winding bywhich the voltage applied to the second mentioned winding is greaterthan that applied to the first mentioned winding.

5. In combination a milli-volt switch, means responsive to suddentemperature change to produce a very low E. M. F. of a few milli-voltsand connected to said switch to actuate the switch, an electricallyoperated appliance adapted to be actuated from an operative source ofelectrical energy having a much greater E. M. F. output than the saidmeans, a holding circuit for the appliance normally isolated from theoperative source of electrical energy and said switch, a double woundrelay controlled via one of its windings by the actuation of said switchdue to sudden temperature change to'effectively connect saidelectrically operated appliance to said higher E. M. F. source whilsttransferring the load due to said source from said switch to saidholding circuit, means to feed from said higher E. M. F. source anassisting E. M. F. into the switch actuating means when the switch isactuated to bring in the said winding of the double wound relay and saidappliance, the other winding of the double wound relay operating inopposition to and at a greater voltage than the first mentioned windingso as to take charge when the switch is returned to normal condition,means to feed from said higher E. M. F. source an assisting E. M. F.into the switch actuating means when said second mentioned winding isbrought into operation and the switch is actuated to cut out saidappliance, and means to regularly interrupt the current supply from saidoperative E. M. F. source to the said switch and the said loadtransferring means, a test circuit, a manually controlled switch tobring in said test circuit for testing the appliance actuating circuit,a resistor in series with the means producing the said low E. M. F. butnormally short circuited, said test switch removing said short circuitand thereby introducing in the low E. M. F. producing means circuit anE. M. F. equal to its predetermined switch operating output, a leadacross said resistor and the first mentioned winding to negative and arelatively much higher resistance in said lead.

6. In a fire warning apparatus the combination of a plurality ofmilli-volt switches, thermocouples adapted to be located at a pluralityof independent possible fire outbreak sources and connected to saidswitches to actuate one of the switches upon a sudden temperature riseat one of said sources, an electrically operated warning device commonto all of said switches adapted to be connected to and actuated from anormal operative source of electrical energy common to all of saidswitches and having a much greater E. M. F. output than thethermo-couples, a double wound relay and a holding circuit with eachswitch, said double wound relay being adapted to connect via one of itswindings said warning device to said operative source and being adaptedto be fed from said operative source, means controlled by the actuationof each switch due to sudden temperature change to effectively connectthe said winding of the associated said double wound relay momentarilyvia the associated 11 switch moving contact tovv said higher E. M. F.source and thereupon to isolate said moving contact from said higher E.M. F. source and maintain the said holding circuit in operation means tofeed from said higher E. M. F. source an implementing E. M. F. into themeans actuating the switch when the switch is actuated to bring in. thesaid warning device, the other winding of the double wound relay beingconnected to said operative source and the switch so as to receive agreater E. M. F. than the first mentioned winding so as to override thefirst mentioned winding to break the. holding circuit when the switch isreturned to normal, and means feeding an assisting E. M. F. into theswitch actuating means when the. second mentioned winding is broughtinto circuit.

'7. A. fire warning apparatus according to claim 6 including anauxiliary thermo-couple set to respond to gradual changes in temperatureand in series connection with other thermo-couples which respond only toa sudden rise in temperature.

8. Electrically operated apparatus for bringing into operation inresponse to a. predetermined change in temperature at a remote source awarning device or other electrically operated appliance, comprising anoperation initiating circuit, a. highly sensitive switch in said circuitand also means adapted to be positioned at said remote source andsusceptible to the influence of a predetermined form of change inambient temperature at said remote source so as to change the electricalcharacteristics of said initiating circuit to actuate the switch, a mainholding circuit adapted to be connected to an available normal source ofelectrical energy and to be closed via said switch consequent upon a.predetermined change in said ambient temperature for maintaining theoperation of the warning device or other appliance. independently oftheoperation initiating circuit, means actuated consequent upon closing.of said holding circuit to relieve the switch of the electrical load dueto the holding circuit and to bring into the main holding circuit thewarning device or other appliance, means to introduce an assisting E. M.F. into the switch actuating means to ensure positive actuation of theswitchduring closing of the holding circuit due to said ambienttemperature reachin a predetermined. critical measurement, and alsomeans to introduce an. assisting E. into the switch actuating meansduring release of said holding circuit due to a change from saidcritical temperatureat the said. remote source.

9. Apparatus. according to claim 8 wherein said switch has a movingcontact of very light form and anactuating coil and a. hair springsimilar to a milli-volt meter, and a normal conditions contact andaholding circuit contact, the coil being connected to the output of themeans adapted to change the characteristics of the operation initiatingcircuit, and the moving contact being connected to the holding circuitvia the hair spring.

10. Apparatus according to claim 8 wherein the switch has two fixedcontacts which are engaged alternately by a moving contact of very lightform actuatedby the low E. M. F. developed due to temperature change atthe remote source, said fixed contacts being connected. to a doublewould relay having two oppositely wound windings, one of these windingsoperatin contacts to bring in the holding circuit and being connectedacross the fixed contact which brings in the hold- 12 ingcircuit whenengaged by the moving contact and a return lead or" the normalelectrical energy supply source, the moving contact being connected tothe positive or supply lead of said normal source, the other winding ofthe double wound relay acting as a release winding and actuating a pairof contacts via which it is connected at one end to the other or releasefixed contact of the switch its other end being connected to positive ofthe normal supply, the contacts of the first mentioned winding breakinginadvance of the contacts of the second mentioned winding when theswitch is returned to normal, said release fixed contact being connectedvia the moving switch contact via a lead including a resistor inparallel with the switch actuating coil and the thermo-couple or saidtemperature responsive sensitive means in the said remote source, therelease winding upon engagement of the moving contact with the releasefixed switch contact having a higher voltage applied across it than theother winding so as to override the latter winding to cause the doublewound relay to release so that the only electrical energy flowing in theinitiating circuit can now be only that due to the thermocouple of lowE. M. F. generating means in. the said remote source.

ll. Apparatus according to claim '7 wherein the said means which changesthe electrical characteristics in the operation initiating circuitdevelops an E. M. F- of only a few milli-volts to operate the switch isadapted to respond effectively to rise in temperature at the said remotesource only when said rise is very sudden.

12. Apparatus according to claim 11 wherein said means comprises athermo-couple device with two coupled points Or zones of generation oflow E. M. F- one or which is so shrouded that whilst during gradualambient temperature changes they respond identically and cancel eachother out, there is an advance in the response of the unshrouded pointor zone. relative to the shrouded one when there is a very pronouncedsudden change in the ambient temperature, e. g. upon the outbreak offire in close proximity to the device, to cause. a development of a lowE. M. F. sufficient'to actuate the switch.

13.. In combination a milli-volt switch, comprising two fixed contacts,a. very light swinging pointer contact adapted to engage alternately thefixed contacts, a hair spring to actuate said swinging contact in onedirection, a moving coil adapted to actuate the swinging contact. in.the other direction, means responsive to sudden temperature change toproduce a very low E. M. F. of a few milli-volts and connected to saidcoil of theswitch to actuate the SWltCh,.'a, holding circuit, anelectrically operated appliance. in said holding circuit adapted to beactuated from an operative source of electrical energy having. a muchgreater E. M. F. output than the said means, said holding circuit beingnormally isolated from its operative source of electrical energy andfrom said. switch, means controlled by the, actuation of said. switchdue to very sudden temperature change. to close said holding, circuitand eifectively connect said electrically operated appliance to-saidhigher E. M. F. source whilst transferring the. load due to saidsourcefrom said switch to said holding circuit, means to feed from saidhigherv F. source an assisting E. M. F. into thesaid coilof the switchwhen the-swinging contact engages one of said fixed contacts to bring inthe said appliance and when it' engages the other fixed contact to cutout said appliance, and

13 means to regularly interrupt the current supply from said operativeE. M. F. source to the said switch and the said lead transferring meansso that the switch contacts are only very momentarily included in theholding circuit.

14. In combination a mulli-volt switch, an operation initiating circuitincluding said switch, means to develop a very low change in E. M. F. ofa few milli-volts in said circuit to actuate the switch, said switchembodying two fixed contacts and a very light swinging contact adaptedto alternately engage the fixed contacts, a hair spring to actuate saidswinging contact in one direction, a moving coil adapted to actuate theswinging contact in the other direction against the influence of saidhair spring, electrically operated apparatus, a main circuit to connectsaid apparatus via said switch to a main source of E. M. F. having amuch greater E. M. F. than the E. M. F. feeding the operation initiatingcircuit, means to introduce an assisting E. M. F. into said operationinitiating containing circuit from said main source to assist the saidcoil at each moment of contact of the switch and comprising theintroduction of a resistor across said main circuit and one end of saidcoil, and means to isolate the switch from the main circuit when themain circuit is closed and to maintain such main circuit closedindependently of, said switch.

15. In combination a thermo-couple chain including a number ofthermo-eouple devices each having a pair of thermo-couples both exposedto the influence of normal ambient air conditions but having one moreexposed than the other so that it will be affected first by the efiectof a very sudden change in ambient temperature, a switch having twofixed contacts (normal and main respectively), a very light movingcontact to alternately engage the fixed contacts, a hair springactuating the moving contact in one direction, a moving coil connectedin series with said thermo-couple chain so that it is energised tooperate the moving contact in the opposite direction against theinfluence of said hair spring by the very low M. F. developed in thechain due to a sudden rise in temperature, a relay, a main circuitadapted to be connected by said relay via said switch to a main sourceof E. M. F. when said coil is energised to move the moving contact intoengagement with said main contact, means to isolate the switch from themain circuit immediately the said connection to the main source of E. M.F. has been effected by the moving and main contacts and to maintain themain circuit closed, means energised from said main source to implementthe E. M. F. ob-

tained from the thermo-couple chain to operoverriding the aforesaidrelay and breaking said main circuit.

16. In combination a thermo-couple chain including a number ofthermo-couple devices each having a pair of thermo-couples both exposedto the influence of normal ambient air conditions but having one moreexposed than the other so that it will be effected first by the cffeetof a very sudden change in ambient temperature, a switch having twofixed contacts (normal and main respectively), a very light movingcontact to alternately engage the fixed contacts, a hair springactuating the moving contact in one direction, a moving coil connectedin series with said thermo-couple chain so that it is energised tooperate the moving contact in the opposite direction against theinfluence of said hair spring by the very low E. M. F. developed in thechain due to a sudden rise in temperature, a relay, a main circuitadapted to be connected by said relay via said switch to a main sourceof E. M. F. when said coil is energised to move the moving contact intoengagement with said main contact, means to isolate the switch from themain circuit immediately the said connection to the main source of E. M.F. has been effected by the moving and main contacts and to maintain themain circuit closed, a resistor across said main circuit and one end ofsaid coil and in series parallel connection with said chain, so that atthe moment of engagement of the moving contact with said main contactpart of the current flow due to the main source flows through theresistor and part through the thermo-couple chain to the moving coil ofthe switch to introduce an implementing E. M. F. into said coil, andmeans energised from said main source adapted to override said relay andbrought into the main circuit when the moving contact is returned to thenormal contact due to a drop in said ambient temperature and to reversethe direction of the said assisting E. M. F. through said seriesparallel circuit to assist the operation of said spring.

17. Electrically operated apparatus for bringing into operation byreason of a sudden change in temperature at a control source a warningor other electrically actuated device, comprising a very sensitiveswitch operable by an E. M. F. of a few milli-volts, means responsive tosudden temperature change to produce a very low E. M. F. of a fewmilli-volts and connected to said switch to actuate the switch, anelectrically operated warning or other electrically operated deviceoperated from a source of electrical energy having a much greater E. M.F. output than the said means, a holding circuit for the said devicenormally inoperative, means controlled by the actuation of said switchdue to sudden temperature change to efiectively connect saidelectrically actuated device to said higher E. M. F. source whilsttransferring the load due to said means controlled by the actuation ofsaid switch from said switch to said holding circuit, and means to feedfrom said higher E. M. F. source an assisting E. M. F. into the switchactuating means.

18. Apparatus according to claim 17 wherein the said means responsive tosudden temperature change to produce a very low E. M. F. comprises athermo-couple device with two coupled points or zones of generation oflow E. M. F. one of which is so shrouded that whilst during gradualambient temperature changes they respond identically and cancel eachother out, there is an advance in the response of the unshrouded pointor zone relative to the shrouded one when there is a very pronouncedsudden change in the ambient temperature, e. g. upon the outbreak offire in close proximity to the device, to cause a development of a lowE. M. F. suiiieient to actuate the switch.

19. Apparatus according to claim 17 including said means to produce avery low E. M. F. and the switch an E. M. F. approximately equal to theoutput of said circuit obtaining when the switch is actuated normally bythe very low E. M. F. due to the sudden rise in temperature.

20. Apparatus according to claim 17 including means which returns thesaid switch to normal circuit broken position when the temperature atthe control source returns to below the predetermined operativetemperature.

WILLIAM HARRY RUFFLE.

16 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 1,443,165 Brown Jan. 23, 19232,127,343 Parlett Aug. 16, .1938 2,219,391 Jacobson Oct. 29, 19402,376,920 Jones May29, 1945 2,473,940 Clark June 21, 1949

